Fungal Dextranase for the Sugar Cane Industry

Introduction

Leuconostoc sp. bacteria are often found associated with deteriorated or sour sugar cane. This microbe has the ability to synthesize alpha-glucan polysaccharides (dextran) from the sucrose released from cane following stalk damage and/or harvesting delays. The level of dextran synthesized varies with the geographic location and climate of the growing area, cane variety, quality of cane, burn-to-harvest time, method of harvesting and cut-to-crush time.

When the dextran level in sugar cane juice exceeds approximately 1000 mg/kg (Brix basis), this high molecular weight polysaccharide increases the viscosity of the sucrose solutions in the milling and refining processes. Dextran interferes with insoluble particle aggregation and settling, filtration rates, evaporation and boiling rates, and overall process control. During evaporation the dextran concentration increases which interferes with crystal formation and crystal separation. This increases sucrose loss to the final molasses. Processing capacity and yields are decreased and plant shutdown may be required for equipment cleaning.

The application of Dextranfree dextranase can alleviate the processing and product quality problems associated with dextrans in sugar milling and refining.

Description

Dextranfree fungal dextranase (E.C. 3.2.1.11, 1,6-alpha-D-glucan 6-glucanohydrolase) is obtained by the controlled fermentation of Chaetomium erraticum var. The enzyme is an endo-dextranase capable of randomly hydrolyzing the interior alpha-1,6-glucosidic linkages of dextran and its degradation products. This activity rapidly reduces the viscosity of dextran solutions, The initial hydrolysis products of Dextranfree dextranase are soluble polysaccharides and oligosaccharides of varying lengths. Prolonged hydrolysis with Dextranfree dextranase results in the formation of glucose and lower levels of isomaltose and isomaltotriose.

Dextranfree dextranase has a high degree of specificity for the interior bonds of the dextraii polymer versus the end sugar unit. Dextranfree also has a pH optimum appropriate for application to mixed juice, high thermal stability and no invertase activity. Dextranases from most other organisms do not have this unique and desirable combination of characteristics.

Properties

Activity:     22,000 DU/ml

Form:         Non-viscous Liquid

Color:        Amber to Light brown

Odor:        Free of Offensive Odor

Taste:        Free of Offensive Taste

Solubility:  Miscible with Water

Effect of pH

Dextranfree exhibits maximum activity at pH 5.0 - 6.0 and can be utilized over the range pH 4.0 - 8.0.

Effect of Temperature

Dextranfree exhibits maximum activity at 50 - 60C and can be utilized at temperatures up to 80C in the presence of high levels of sucrose.

Activators and Cofactors

No activators or cofactors are necessary for the complete activity of Dextranfree. Dextranfree is inhibited by some metal ions such as copper and mercury.

Solubility

Dextranfree is completely miscible with water. Dilutions of Dextranfree with clean tap water (up to 50 fold) are sufficiently stable over 24 hours at 25C to be used. The enzyme can either be added as a dilute solution or can be added directly.

Substrate

Dextranfree dextranase may be used to hydrolyze dextran in sugar cane, sugar beets and other microbial or synthetic dextrans.

Application

Treatment of Raw Juice

Dextranfree dextranase should be added in the sugar refining process at the earliest possible processing step. In doing so, the enzyme hydrolyzes the contaminating dextran to lower viscosity polymers early in the process, minimizing associated dextran problems in subsequent processing steps.

Raw juice containing dextran can be enzymatically treated between the crushing and clarification processing steps. This requires the use of an appropriate reactor between the primary and secondary heaters. The reactor should be sized to provide adequate hold time for dextran hydrolysis at the maximum process flow rate and sufficient agitation to completely mix the reactor contents. The reactor can either be a tank reactor or a compartmentalized reactor. By preheating to 55 to 60C and partial liming to raise the pH to 5.0 to 5.5, the reactor size and hold time can be reduced.

The application rate of Dextranfree varies with Brix, dextran content of the raw juice, holding time and processing conditions. To optimize the use of Dextranfree we recommend analyzing the raw juice for dextran content and performing a number of trials prior to routine use of the enzyme. This assures an optimum process and uniform product quality. Table I presents Dextranfree use levels which will normally apply for the treatment of raw juice.

Table I - Use Level of Dextranfree in Raw Cane Juice (g/MT Raw Juice)

Treatment Time	Dextran Concentration (mg/kg Brix)
(Minutes)	2,000	5,000	10,000	15,000
15	80	120	160	240
30	40	60	80	120
60	20	30	40	60

pH: 5.0 - 5.5, Temperature: 55 - 60C, Brix: 10 - 20C

The desired level of dextran hydrolysis can be achieved either by adjusting the level of enzyme treatment or by adjusting the hold time. In most situations the hold time will be fixed so that adjustments are made by varying the enzyme application rate.

Treatment of High Brix Syrup

When a holding reactor is not available between the tandems and the clarifiers for the treatment of raw juice, an alternative site for Dextranfree addition must be considered.

In the presence of concentrated, high Brix syrup (65` Brix), Dextranfree dextranase demonstrates extended thermal stability over the temperature range of 60 to 85C. The excellent thermal stability of Dextranfree allows the addition of the enzyme in the last effect of the multiple effect evaporator. Dextran breakdown will occur in the evaporator and in the syrup buffer tank which follows.

For the same reasons mentioned above, trials should be conducted to determine the actual application rates prior to routine use of Dextranfree. Table 2 presents Dextranfree use levels which will normally apply for the treatment of neutral (pH 7.0), high Brix syrups at 55 to 60C.

Table 2 - Use Level of Dextranfree in Syrups (Kg/MT Syrup)

Treatment Time	Dextran Concentration (mg/kg Brix)
(Minutes)	2,000	5,000	10,000	15,000
30	1.6	2.4	3.2	4.8
60	0.8	1.2	1.6	2.4
120	0.4	0.6	0.8	1.2
240	0.2	0.3	0.4	0.6

pH: 7.0, Temperature: 55 - 60C, Brix: 60 - 65C

Table 3 presents Dextranfree use levels which will normally apply for the treatment of neutral (pH 7.0), high Brix syrups at 65 - 85C.

Table 3 - Use Level of Dextranfree in High Brix, High Temperature Syrups (Kg/MT Syrup)

Treatment Time	Dextran Concentration (mg/kg Brix)
(Minutes)	2,000	5,000	10,000	15,000
30	0.8	1.2	1.6	2.4
60	0.4	0.6	0.8	1.2
120	0.2	0.3	0.4	0.6

pH: 7.0, Temperature: 65 - 85C, Brix: 60 - 65C

Sugar Refining

When high dextran content is a problem in the refining of raw sugar, Dextranfree can be added to the remelt tank.

Storage Stability

In sealed containers, under cool, dry conditions, the loss in activity of Dextranfree liquid is normally less than five percent in six months. Storage life can be extended by storing under refrigeration at 5C.